Electrodepositing metals



Patented July 21, 1936 UNITED STATESfPATENT OFFICE ELECTRODEPOSITINGMETALS Charles Joseph Brockman, Athens, Ga.

No Drawing.

12 Claims.

plied. Unfortunately, the coating so formed is 5 nearly always of aspongy, poorly adherent nature and serves only to prevent the adherenceof the deposit later to be made.

In order to avoid the formation of this poorly adherent deposit a numberof modifications of some are now in use. In general these modificationsfall into two classes. Either the object to be plated is first coveredwith an intermediate or strike coating of a metal that will form an ingdeposited on the surface so formed, or the plating conditions are somodified that the metal with which it is desired to plate will not forma spongy deposit of the kind mentioned.

Various changes in plating conditions have been tried, including thestarting of the deposition at hating the spongy coating, the cyanidebaths are I probably the most common. Copper can be directly plated uponiron or steel from an alkaline copper cyanide solution, although thecathode efliciency is relatively poor, the bath is extreme- 1y poisonousand the current density must be carefully controlled. Usually a thin"strike" coating of copper, is applied by the use of a cyanide solution.and the plating then finished in a copper sulfate bath. Other metalsmay be similarly deposited by the, use of cyanide baths upon cathodeson. which they will not ordinarily form an the basic plating procedureshave been tried and,

adherent deposit on the object and the final coat- Application January21, 1935, Serial No. 2,837

adherent deposit. However, the disadvantages of plating from a cyanidesolution are much the same regardless of the metal plated.

Because of these disadvantages at least several additional types. ofbaths have been developed and 5 tried under various conditions. Of thesemention may here be made of two, the tartrate bath and the oxalato bath,both used for plating copper on steel or iron. A tartrate bath suggestedby Brown and Mathers, J. Phys. Chem. 10 39-51 1 (1906) has the followingformula:

Copper sulfate 60 grams Sodium hydroxide; 50 grams Sodiumpotassiumtartrate 159 grams Water 1 liter 15 The oxala bath was suggested by Finkand Wong, Trans. Electrochem. Soc. 63 Preprint 9 (1933) It is alsoaqueous and has the formula:

Copper oxalato (Disodium dia- 20 qu o d i o xal a t o cuproate)Na2[Cu(CzO4) 2.(H.2O) a] 20 grams/liter Sodium sulfate 15 grams/ literBoric acid 20 grams/liter 2r The authors tell us that their bathsobviate many of the difliculties experienced with the cyanide type ofbath.

Nevertheless, experiments indicate that the current efliciency, qualityof the deposit and other features of the methods using these baths arestill subject to improvement. Hence, it is the purpose of the presentinvention to provide a new method involving the use of a new bath andthus to obtain greater current efficiency, use lower current densitiesif desired, and yet to form a uniform adherent deposit from anon-poisonous bath. The new bath also has excellent throwing power andhence is especially well adapted to the plating of irregularly shapedarticles. Further objects and advantages of this invention will ap-.pear from a consideration of the following description of the new bathand the manner of its use. 1

According to the discovery upon which this invention is predicated itappears that triethanolamine, and probably other similar compounds,formwith metals complexions somewhat similar, but more advantageous, intheir affect in plating baths to the corresponding cyanides. Bathscontaining these lens may be used with particular advantage in theelectrodeposition of metals upon cathodes on which the metals will notsatisfactorily plate from the common plating solutions. Such baths arenon-poisonous and plate satisfactorily throughout a wide range of Coppersulfate (51-120) 150 grams/liter Boric acid grams/liter Triethanolamine2'70 0. c./liter This bath was compared with an aqueous cyanide bathconsisting of:

Cuprous cyanide 22.5 grams/liter Sodium cyanide 34.0 grams/liter Sodiumcarbonate 15.0 grams/liter The results with the solutions stirred duringdeposition and run at 30 amperes per square foot, 5

1 volts potential were as follows:

Copper deposited mg./sq. cm. Time in seconds 0 id yan 0 New bath bath in68 01c 30 3. 27 .138 50 6. 69 220 70 7. 74 324 90 l 9. 38 428 120 '11.91 601 The deposit formed by the new process was bright,

hard and copper colored. It was found preferable I to use copper anodesto keep the-solution supplied with the metal.

A modification of this bath that has proved particularly advantageousbecause of the high current efficiency that may be obtained therewithand because the deposit therefrom is especially satisfactory as a.strike plate upon which further quantities of metal may be deposited hasthe following formula:

Copper sulfate (51120) 16 grams/liter,- Sodium oxalate 1O grams/literTriethanolamine 22 c. c./liter The solution so formed is light blue anddoes not plate on iron by contact. A current density of 3.6

amperes per square foot at 1.5 to 2.5 volts gives I. bright plateon-steel which will hold copper from the ordinary copper sulfate bath.-Below are figures showing three test depositions under these conditions.They may be compared with the figures given above, but it should beremembered that the current density here is only aboutoneeighth of thatused in obtaining those figures.

Copper deposited Tim in mgJsq. cm. seconds I,

' All deposits of 50 seconds or over from this bath were capable ofholding a plate from an acid sulfate bath and deposits of '70 seconds orover were particularly well suited to this purpose.

As another example of the general principlesor 5 the inventiontheplating of nickel on zinc. may be mentioned. Nickel will notordinarily form an adherent deposit on zinc. However, good deposits onzinc can be obtained by the use of any one of several solutionscontaining a nickel salt and tri ethanolamine. The following solutions,which have been tried and found satisfactory may be cited asillustrative. Good throwing power is a characteristic of the solutionsso that the deposit is smooth and uniform even though the cathode isirregularly shaped.

Nickel ammonium sulfate 120' grams/liter, Triethanolamine 200 c.c./liter Water Remainder 20,

(Boric acid may be added in small amounts but seems to have noappreciableeifect.)

Still further examples are furnished by the following aqueous solutionsused for plating zinc, cobalt and cadmium respectively on copper, orother metals:

Zinc sulfate (71-120) 75 trams/liter Triethanolamine 25 c. c./literWhite precipitate filtered out before use.

Cobaltus sulfate 75 grams/liter Triethanolamlne c. cJIi'ter Currentdensity 17 amps/sq. dm. Cobaltous nitrate (61-120) 75 grams/literTriethanolamine 50 c.c./liter Current density l 25 amps ./sq. dm. 50Cobaltous sulfate (611:0) 75 grams/liter 'lriethanolamine 125 c. c.lliter Current density 11 amps./sq. dm.

Plates well on zinc. 55 Cadmium sulfate '15 grams/1i Triethanolamine 25c. c./liter White precipitate filtered out .before use;

Cadmium nitrate (4Ha0) 75 grams/liter 6o Triethanolamine 25 c. c./literCurrent density; 11 to 22 amps/sq. dm.

' White precipitate filtered out before use.

While the invention has been described specifically by examples usingtriethanolamine in 65 I formulas in order to give a concreteunderstanding thereof, it is to be understood that aosasc receive thedeposit. Also. although the invention is most advantageously used wherethe metal will not plate in an ordinary acid bath it may be used eventhough the metal will so plate when for any other reason it may bedesired to plate the metal from the new type of solution.

As an example of the compounds that may replace triethanolamine in thepractice or this invention diand mono-ethanolamine may be mentioned andthe use or other hydroxy alkyl amines .and their substitution productsand homologues particularly those having properties fis similar totriethanolamine are also contemplated. Other changes may be made toadapt the principles of this invention to various technical situationsall within the skill oi! the chemist and the broadest scope of thisinvention.

We claim;

1. A method of electroplating that comprises contacting the'obiect to beplated with a solution containing the metal to be deposited and anethanolamine, and passing an electric current through said solution'andobject to deposit the .metal thereon.

, 2. A method of electroplating that comprises contacting the object to,be plated with asolution containing the metal to be deposited and analkylolamine'and passing an electric current through said solution andobject to deposit the metal thereon.

x 3. A method of electroplating that comprises contacting the object tobe plated with a solution containing the metal to be deposited and atrialkylolamine and passing an electric current through said solutionand object to deposit the 5. A method of electroplating that comprisesand an alkylolamine and an electric cur rent through said solution andobject to deposit the metal thereon.

6. A method of electxodepositing copper that comprises contacting theobject to be plated with a solution containing copper and analkylolamine,

and passing an electric current through the solution and object todeposit the'copper thereon.

'l. A method oif electrodepositing copper that comprises contacting theobject to be plated with a solution containing around 150 grams perliter oi copper sulfate and around 270 c. c. per liter oftriethanolamine, and passing an electric current,

through the solution and object to deposit the copper thereon.

8. A methodof electrodepositing copper that comprises contacting theobject to be plated with a solution containing around 16 grams per literof copper sulfate, around 10 grams per liter of sodium oxalate andaround 22 c. e. per liter of 20 triethanolamine. and passing an electriccurrent through the solution and object to deposit the copper thereon.

9. A method of electrodepositing copper on iron that comprisescontacting the iron with a solution containing copper, an oxalate andtriethanolamine and passing an electric current through the solution andiron to deposit copper on the iron.

10. A method of electroplating that comprises contacting a zinc objectto be plated with a solu- =tion containing nickel ammonium sulfate andaround 100 to 200 c. c. per liter of triethanolamine and passing anelectric current through said solution and object to deposit the nickelthereon.

11. A method oi! electroplating zinc that comprises contacting theobject to be plated with a solution containing zinc and triethanolamine,and passing an electric current through the solution and objectto'deposit the zinc thereon.

12.. A method of electroplatingthat comprises contacting a zinc objectwith a solution containing nickel and triethanolamine and passing anelectric current through the solutionto deposit the nlckel'thereon. I

JOSEPH BROCKMAN.

